Rates of lifetime drug use and dependence among repeat offenders in this sample were higher than the rates in other samples of repeat DUI offenders (Lapham et al., 2006; Laplante et al., 2008). The differences in prevalence rates between our study and those of previous DUI studies may result from our sample selection of families at high risk for alcohol dependence, which may also have correlated high risks for drug dependence (Kendler, Prescott, Myers, & Neale, 2003). The individuals recruited from treatment programs for DUI offenders in earlier studies may have had fewer or more varied familial vulnerabilities to substance use disorders. Differences in rates of drug use may also be due to reporting differences. Because individuals in earlier studies were recruited from treatment settings where they’d been referred due to DUI legal problems, they may have been reluctant to report drug use for fear it might add to their existing legal troubles. By contrast, the DUI variable in this study was based on self report rather than arrest records, and individuals may have been more willing to accurately report drug use.
